1. Field of the Invention
The present invention relates to a method of making a diffraction grating device in which an optical waveguide is irradiated, by way of a phase grating mask, with light capable of inducing a refractive index modulation in an optical waveguide region of the optical waveguide so as to form a diffraction grating in the optical waveguide region; the diffraction grating device made by this method; and an apparatus for making the diffraction grating device.
2. Related Background Art
Diffraction grating device comprises a diffraction grating formed in an optical waveguide region of an optical waveguide (e.g. an optical fiber, planar optical waveguide, and the like) and is used as an optical filter and the like. Such a diffraction grating device is manufactured as follows. Namely, by way of a phase grating mask, an optical waveguide is irradiated with a predetermined wavelength of light capable of inducing a refractive index modulation (which is ultraviolet light in general, and will hereinafter be referred to as “refractive index modulation inducing light”) Then, interference fringes of the refractive index modulation inducing light are generated in an optical waveguide region of the optical waveguide. Hence, the refractive index at a predetermined part of the optical waveguide region provided with the interference fringes is modulated, whereby a diffraction grating is formed.
Here, laser light emitted from a light source such as a KrF laser light source, which outputs the refractive index modulation inducing light, has a luminous flux diameter smaller than the length of the diffraction grating device to be manufactured. As a consequence, a diffraction grating device having a desirable length is made when the refractive index modulation inducing light is made incident on the diffraction grating while being scanned longitudinally of the optical waveguide.